Ginkgo Flavone Glycosides & Terpene Lactones: The 24/6 Standard

Written and reviewed by Dr. Xiaoyan Qiu · Botanical Extract R&D Engineer, Valeherb · June 2026

The “24/6 standard” is the most cited specification in ginkgo biloba sourcing — 24% flavone glycosides and 6% terpene lactones. Most buyers have seen the numbers. Fewer understand why both are required, why they are measured differently, or what goes wrong when a COA shows only one of them. The 24 and the 6 are not two ways of measuring the same thing; they describe two chemically distinct compound classes with different mechanisms, different analytical methods, and different quality failure modes. This article explains what each fraction is, how it is measured, why the measurement method matters more than it looks, and what a complete COA for a 24/6 extract should actually show.

Two Compound Classes, Two Different Roles

Standardized ginkgo biloba extract contains hundreds of compounds, but the 24/6 specification targets two fractions that are analytically tracked and clinically referenced. They are grouped together on a COA, but they are not related chemically or mechanistically.

Flavone glycosides are polyphenolic compounds — specifically flavonol-O-glycosides built from quercetin, kaempferol, and isorhamnetin conjugated to sugar units. They are the antioxidant fraction of ginkgo extract, studied for free-radical scavenging activity in neuronal tissue.^[1] Flavonoids of this type are found across many plants; they are not unique to ginkgo.

Terpene lactones are structurally unique to Ginkgo biloba — no other commercially significant plant produces them in quantity. They divide into ginkgolides (A, B, C, J) and bilobalide, with the ginkgolides studied for platelet-activating factor inhibition and bilobalide studied for neuroprotective activity through separate pathways.^[2] The uniqueness of the terpene lactone fraction is also why it is the harder target to fake — flavone glycosides can be spiked into an extract using external flavonoid sources, but terpene lactones cannot be substituted without the actual ginkgo-derived material.

Why They Are Measured by Different Methods

The two fractions require different analytical approaches because they have different chemical properties — and understanding this difference is what makes a COA readable rather than just a set of numbers to accept at face value.

Flavone glycosides absorb strongly in the ultraviolet range, which makes UV spectrophotometry a workable detection method after an acid hydrolysis step. The hydrolysis converts the glycosides to their aglycone forms (quercetin, kaempferol, isorhamnetin), which are then quantified by UV and converted back to glycoside weight using correction factors.^[3] This is the standard Ph. Eur. method. The limitation is that the hydrolysis step measures aglycone sum rather than the individual intact glycosides — which is why flavone glycoside content is vulnerable to adulteration with external quercetin or kaempferol sources that release the same aglycones on hydrolysis.

Terpene lactones do not absorb UV light, which means the UV method used for flavone glycosides simply cannot detect them. They require HPLC with either refractive index detection, evaporative light scattering detection (ELSD), or mass spectrometry detection — each more demanding analytically than UV spectrophotometry.^[4] This is why terpene lactone content is a stronger authenticity indicator than flavone glycoside content: a supplier cannot inflate the terpene lactone number without the actual ginkgo-derived compounds, whereas the flavone glycoside figure can be manipulated with cheaper external sources.

Why 24% Alone Is Not a Complete Specification

The most common specification error in ginkgo procurement is requesting “ginkgo biloba extract 24%” without specifying terpene lactone content. From a supplier’s perspective this request is easy to satisfy — flavone glycoside content is the simpler of the two measurements, and it is the number most prominently displayed on product sheets. But it leaves the second, more chemically distinctive fraction entirely unverified.

Studies examining commercial ginkgo products have found significant variation in terpene lactone content even among products claiming to meet the 24% standard, with some products falling below the 6% threshold while hitting the flavone glycoside target.^[5] The 24% figure and the 6% figure are independent of each other — a batch can pass one and fail the other, and without both measurements on the COA, a buyer cannot know which situation they are in.

The three-part specification that defines EGb 761-type material — 24% flavone glycosides, 6% terpene lactones, ginkgolic acid <5 ppm — exists precisely because each element catches a different failure mode. The flavone glycoside figure confirms the antioxidant fraction. The terpene lactone figure confirms the ginkgo-specific fraction that cannot be substituted. The ginkgolic acid limit confirms that the cytotoxic alkylphenols present in raw leaf have been adequately removed. All three together define a complete, verifiable composition. For how this translates to the EGb 761 reference standard used in clinical research, see our guide to EGb 761 and the ginkgo reference standard.

How to Read the Terpene Lactone Section of a COA

A total terpene lactone figure of 6% is the minimum — but for premium applications, the breakdown within that 6% matters. The Ph. Eur. specification sets sub-ranges: ginkgolides A, B, and C combined at 2.8–3.4%, and bilobalide at 2.6–3.2%.^[2] Bilobalide typically accounts for roughly half the total terpene lactone fraction, which means a 6% total can represent very different ginkgolide contents depending on how much bilobalide is present. Or learn about Excarepharm’s definition of the Ginkgo Biloba Leaf Extract industry standard.

For the specific role of ginkgolide B — the most extensively studied individual terpene lactone for PAF inhibition — and why it warrants separate confirmation in premium formulas, see the full breakdown in our guide to ginkgolide B and the terpene lactone fraction.

The Adulteration Risk and Why Terpene Lactones Matter More Than They Look

Ginkgo biloba is one of the most commonly adulterated botanical ingredients in the supplement market. Because the flavone glycoside measurement involves hydrolysis to aglycones, a COA showing 24% flavone glycosides can be achieved by spiking cheaper external flavonoid sources — rutin, quercetin, or other flavonol-containing plant extracts — into a low-quality base.^[3] This is well-documented: studies examining commercial ginkgo products have identified adulteration with rutin and quercetin that passes the 24% threshold while the underlying ginkgo content is substantially diluted.

Terpene lactones cannot be faked in the same way. Because ginkgolides and bilobalide are chemically unique to ginkgo and require HPLC with non-UV detection, a product that meets the 6% terpene lactone target on a per-batch COA is almost certain to be genuinely derived from ginkgo leaf. This is why the terpene lactone result — not the flavone glycoside result — is the stronger authenticity indicator for a complete 24/6 extract. For sourcing decisions where authenticity is a concern, the terpene lactone COA figure is the one that carries more weight.

The full sourcing specification, available grades, and batch documentation requirements are on the Valeherb ginkgo biloba extract product page.

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